Field of the Invention
The invention relates to a shock wave source, particularly, useful for a lithotriptor, including a pressure source for the generation of a pressure wave pulse, a focusing device for focusing the pressure wave pulse and a seal diaphragm for coupling the pressure wave pulse into a body.
Such a shock wave source is know, for example, from German Patent Publication No. 33 28 051. As shown therein, a pressure source is provided in the form of a shock wave tube which transmits a pressure wave pulse. The pressure wave pulse traverses a prepassage space to a focusing device which is, for example, fashioned as a lens. After the focusing device, the pulse traverses a coupling space before it is coupled into the body of a patient via a seal diaphragm. In this case, it is used for lithotripsy, that is, the fragementation of concrements, such as kidney stones.
A shock wave source of the above mentioned kind is furthermore known from German Patent Publication No. 33 12 014. There, the pressure source and the focusing device are combined. The coil of the pressure source is of concave shape so as to generate an already focused pressure wave pulse. The focusing device has a natural or geometric focus at the site wherein the concrement to be fragmented is placed. By the time it has reached the focus, the pressure wave pulse has developed into a shock wave pulse.
Experimentation has shown that in general the following applies: If up to a distance of approximately one-half wavelength from the geometric focus no shock wave has formed, on the basis of diffraction limitation, no further focusing and thus no formation of shock wave up to the focus can take place. The wavelength results thereby from the duration of the fundamental oscillation associated with the instantaneous pressure wave pulse. Experiments have further shown that the pressure wave pulse must have a given minimum value for the ratio of amplitude to build-up time at the focusing device in order that a shock wave can form at all. In order to achieve this minimum value for the quotient given by the geometry and customary filling with water of the prepassage space, it is necessary to generate a pressure wave pulse with a relatively high amplitude at the site of the focusing device. From the point of view of the equipment, this is decidedly a disadvantage for the life expectancy of the pressure source, for example an electromagnetic coil, and the electrical insulation expenditure is considerable. From a medical point of view, the relatively high stress placed upon the patient due to a high dose of acoustic energy, is undesirable.
It is an object of the present invention to design a shock wave source of the above-mentioned kind in such a way that the above-noted negative effects are reduced.